Highly regio-selective mono nitration of phenols is accomplished using hydrated ferric nitrate as nitrating agent in phosphorous based ionic liquids in particular phosphonium ionic liquids viz, trihexyl (tetradecyl) phosphoniumtetrafluoroborate (PIL-1) and trihexyl (tetradecyl) phosphonium chloride (PIL-2) as the solvents. Trihexyl (tetradecyl) phosphoniumtetrafluroborate (PIL-1) is found to be more suitable even though the nitration rate was low. The higher rate of nitration in case of trihexyl (tetradecyl) phosphonium chloride PIL-2 may be due to high acidity. In particular, excellent paraselectivities were observed for the unsubstituted, orthoand metasubstituted phenols. The quantitative conversion was observed during all reactions making this methodology attractive for synthetic and commercial utility.